Referring to FIG. 1, one of the key elements in an RF/Microwave radio 10 is a T/R (Transmit/Receive) Switch 22. T/R Switch 22 is one component in a Front End Module (FEM) 16. The other components are power amplifiers (PA) 18 and low noise amplifiers (LNA) 20. For time division duplexing (TDD) systems, T/R Switch 22 couples an antenna 24 to PA 18 via an electrical connection 26 during a data/voice transmit mode, and couples antenna 24 to LNA 20 via electrical connection 28 when in data/voice receive mode. T/R Switch 22 provides isolation to the receive section when it is connected to PA 18 during transmit and isolation to the transmit section when it is connected to LNA 20 during receive. T/R Switch 22 is a single-pole double throw (SPDT) type switch that allows connection between antenna 24, PA 18 and LNA 20. A switch connecting multiple PAs and/or multiple LNAs will require a single pole, multi-throw T/R Switch. The T/R Switch IC is typically fabricated in GaAs and is composed of a number of series and shunt FETs (Field Effect Transistors) or HEMTs (High Electron Mobility Transistors).
Referring to FIG. 2, a typical SPdT GaAs RF T/R Switch IC is shown. During transmit mode, the series FETs or HEMT devices on the receive side are off to provide receive isolation and are subject to high voltages when the PA is transmitting at high RF powers (i.e. ˜1 Watt) in a 50 Ohm impedance system. The GaAs FET and HEMT devices have a high breakdown voltage and can sustain the large voltage excursions. For typical silicon IC implementations of T/R Switch 22, the FET devices (i.e. typically NMOS) do not have large breakdown voltages and therefore, a T/R Switch implantation in Si CMOS or BiCMOS can usually only handle very limited RF powers.
One approach for resolving this issue is to use SOI (Silicon on Insulator) IC technology. In SOI technology, the NMOS devices have higher breakdown voltages and therefore a RF T/R Switch topology similar to that shown in FIG. 2 may be implemented for high power applications. However, at present time the cost of SOI technology is somewhat prohibitive and integration with other RF components limited. Thus, presently a need exists for a lower cost and higher integration factor for incorporating a high power (˜1 Watt) RF T/R Switch in traditional Si CMOS or Si/SiGe BiCMOS technology.